It has been known for portable communication devices, such as mobile phones, to be provided with dual subscriber identity module (SIM) cards. Switching between SIM cards, however, traditionally required the mobile phone to be restarted. There has been one recent instance of two radio modems being included in a mobile phone, each modem relating to a different SIM card, thereby allowing two SIM cards to be active simultaneously. Accommodating two active SIM cards in a device presents numerous design challenges.